Using rapid flow microfluorometry for analysis and sorting of cells, aspects of the following projects have been supported during the previous year: 1) characterization of differentiation antigens on murine lymphocytes; 2) analysis of lymphocyte abnormalities in mice prone to autoimmune disease; 3) identification of murine spleen accessory cells, and 4) determination of the quantity and affinity of immunoglobulin Fc receptors on cell surfaces.